External Hard Drive Unreadable After Copying, How to Fix?

So, my school loaned me a Macbook Pro. I copied all the files on it to an external hard drive because I had to turn this Mac back yesterday. But when I copied the apps to the same external hard drive, it won't allow me to do that. Why and how to fix it?

There are several potential reasons for the "external hard drive unreadable after copying" issue. I will list four of them as below:

• Corrupted file system: An external hard drive can be formatted as NTFS, exFAT, or FAT32. The hard drive cannot locate files if these file systems are corrupted.
• Physical damage: You cannot access the stored data once the external hard drive is physically damaged.
• Virus or malware infection: The virus or malware infection may lead to disorder on the hard drive.

Accordingly, multiple solutions can fix this problem:

Method 1. Check File System

The most frequent reason for this issue is a corrupted file system, so the simplest method is to use EaseUS Partition Master to examine and fix a corrupted file system. It has a "Check File System" feature that can help you directly fix the unreadable error of a corrupted hard drive. Here is how to do it:

Method 2. Run CHKDSK to Find Errors

Another method is to run CHKDSK in the Diskpart to find and repair hard drive errors: